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Work done by a constant torque equation DOESN'T give me angular speed Help!

  • #1
Number15.png


What is given:

Torque: τ = 34.5 N * m
Inertia: I = 0.130 kg * m2
Angular speed: ω = ?
Work done by a constant Torque: τΔθ = (1/2)Iωf2 [STRIKE]- (1/2)Iωi2[/STRIKE]
Angular displacement: Δθ = 17.1 rev/s = 107.442 rad/s


τΔθ = (1/2)Iωf2
(34.5)(107.442) = (0.5)(0.130)ωf2
3706.765 = 0.065ωf2
57027.156 = ωf2
238.8 = ω

It's still wrong :(
 
Last edited:

Answers and Replies

  • #2
537
1
Δθ is 17.1 revolutions. You need to convert that to radians.
 
  • #3
Doc Al
Mentor
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1,124
Make sure your angular displacement is in radians, not revolutions.
 
  • #4
993
13
Change 17.1rev's to ... radians's.
 
  • #5
Doc Al
Mentor
44,874
1,124
3x should be enough :biggrin:
 
  • #6
  • #7
Change 17.1rev's to ... radians's.
I just did and it's still wrong
 
  • #8
Doc Al
Mentor
44,874
1,124
  • #9
993
13
If you show your work help may be given.
 
  • #10
Show what you did.
B]What is given:[/B]

Torque: τ = 34.5 N * m
Inertia: I = 0.130 kg * m2
Angular speed: ω = ?
Work done by a constant Torque: τΔθ = (1/2)Iωf2 [STRIKE]- (1/2)Iωi2[/STRIKE]
Angular displacement: Δθ = 17.1 rev/s
Conversion (17.1 x 2 x π) rad/s = 107.442

τΔθ = (1/2)Iωf2
(34.5)(107.442) = (0.5)(0.130)ωf2
3706.765 = 0.065ωf2
57027.156 = ωf2
238.8 = ω
 
  • #11
If you show your work help may be given.
But I just did o_O
 
  • #12
Doc Al
Mentor
44,874
1,124
Looks like they want the speed in rev/s, not rads/sec.
 
  • #13
Looks like they want the speed in rev/s, not rads/sec.
Sooo...I don't convert angular displacement?
 
  • #14
Doc Al
Mentor
44,874
1,124
Sooo...I don't convert angular displacement?
Convert your answer for ω from rad/s to rev/s.
 
  • #15
Convert your answer for ω from rad/s to rev/s.
τΔθ = (1/2)Iωf2
(34.5)(107.442) = (0.5)(0.130)ωf2
3706.765 = 0.065ωf2
57027.156 = ωf2
238.8 rad/s = ω

238.8/2π rev/s = ω
38 rev/s = ω

Awesome :eek:
Thanks!
 

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